This invention relates to an engine management system capable of determining engine phase of a four-stroke internal combustion engine.
When a four-stroke engine is running it is desirable to verify that the fuel is being injected into the cylinder during the correct stroke. If the fuel is injected on the wrong stroke, the engine may still run, but engine emissions will increase and engine efficiency will drop.
Internal combustion engines normally have a crankshaft sensor that provides a rotation signal that can be used to verify piston position over one complete revolution of the engine. However, as the engine takes two full revolutions to complete one cycle of the four strokes, this type of engine sensor cannot distinguish between the two halves of the cycle, sometimes referred to as the charge phase in which the cylinder is charged with air and fuel, and the power phase in which the air fuel charge is ignited and expelled as exhaust gas.
Currently, the most common method of verifying the engine injection stroke is through the use of a camshaft position sensor. However, a camshaft sensor with associated wiring and engine machining adds cost to the engine.
It is possible to achieve engine stoke verification without the use of a camshaft position sensor, for example as described in patent document EP 0 990 787 A. This document describes a method of determining engine stroke in which one cylinder of the engine is made to run for one cycle at non-optimal conditions. This causes a sharp change in the operating conditions for that cylinder, which can then be detected by measuring a momentary change in the composition of the exhaust gas. The time at which the exhaust gas composition changes can then be used to determine the engine stroke on which exhaust gas is expelled by the affected cylinder.
This method suffers from a number of problems, primarily the need to operate the engine in a non-optimal manner and the need for steady state operation before, during and after the test.
The present invention seeks to provide an improved system for engine injection stroke verification.
According to the present invention there is provided an internal combustion engine, comprising a number of cylinders, the or each cylinder containing a four-stroke reciprocating piston, an exhaust conduit, one or more engine operating condition sensors including an exhaust gas sensor in the exhaust conduit for measuring the composition of the exhaust gas, a fuel injection system, and an engine management system for controlling the operation of the engine including the fuel injection system and the air/fuel ratio for at least one cylinder, wherein the engine management system contains engine operation data, the engine operation data being related to expected engine operation with engine fueling on the correct stroke and/or engine fueling on an incorrect stroke, and the engine management system is arranged to:
a) receive from said sensor(s) respective signal(s);
b) oscillate the air/fuel ratio between a relatively rich level and a relatively lean level, the exhaust gas composition varying depending on the air/fuel ratio;
c) reverse the direction of change of the air/fuel ratio when the exhaust gas composition is sensed as being indicative of rich engine operation or lean engine operation;
d) determine the temporal characteristics of the oscillation in the air/fuel ratio; and
e) determine whether or not the engine is being fueled on the correct stroke by comparing said temporal characteristics with said relevant engine operation data.
This procedure provides the advantage that there is no need for a camshaft position sensor, and the engine is no longer required to operate in a non-optimal manner to provide the engine management with the signals required to verify whether or not the engine is being fueled on the correct stroke by comparing.
The term xe2x80x9cengine management systemxe2x80x9d will be understood to mean any electronic system capable of controlling or influencing the operation of the engine.
The term xe2x80x9ctemporal characteristicsxe2x80x9d should be understood as meaning period or frequency or any other time dependent characteristic that could be used to characterise an oscillating system.
It should be understood that the term xe2x80x9cmeasure exhaust gas compositionxe2x80x9d means to measure one or more of the composition characteristics of the exhaust gas composition such as the concentration of one or more of the component gases.
In order to meet modern emission standards, engine control systems utilize a form of closed loop control to control the air/fuel ratio of the cylinder charge. The use of closed loop control is dictated by the use of three way catalytic converters which require very accurate control of the air/fuel ratio around a stoichiometric value in order to operate at their maximum efficiency. Closed loop control uses feedback from a sensor at an output from a system to control an input to the system that affects the signal from the output, sensor. In this case the output sensor measures the exhaust gas composition and the engine management system varies the air/fuel ratio accordingly. In open loop control the engine management system does not take account of the signal from the exhaust gas sensor when setting the air/fuel ratio. Open loop control may occur, for instance, when the driver presses the throttle.
A simplified model of a three way catalyst is that of an oxygen storage device. When the engine air fuel ratio is lean, the exhaust gas is rich in NOx gases and the oxygen storage sites in the catalyst remove the oxygen in the NOx gasses to create harmless N2. Some of the excess oxygen in the exhaust gases is also stored in this phase. When the air fuel ratio is rich, the exhaust gases are rich in hydrocarbons HC, CO and H2. The oxygen stored on the catalyst is then released to react with these gases to form CO2 and H2O.
To measure the exhaust gas composition, it is common to use a Heated Exhaust Gas Oxygen (HEGO) sensor. Commonly available HEGO sensors have a steep change in output around the oxygen concentration resulting from near stoichiometric air/fuel ratio. This results in the HEGO sensor being used in a bi-stable manner to detect either rich or lean combustion, rather than provide an absolute indication of air/fuel ratio.
In a closed loop feedback system this bi-stable HEGO sensor is ideally suited to a limit cycle operation oscillating the air/fuel ratio about the stoichiometric value. The present invention takes advantage of the fact that there is already a slight oscillation in engine operating conditions to determine whether or not the engine is being fueled on the correct stroke. For this invention to be applicable there is no need for the engine to be fitted with a catalyst, but the invention is particularly suited to an engine that does have a catalyst fitted.
The engine management system may calculate a transport delay time from the period or frequency of the reversal of the oscillation in the air/fuel ratio, this being indicative of the time taken for a change in engine operating conditions to alter the composition of the exhaust gas at the exhaust gas sensor. This transport delay, time may then be compared with the engine operation data stored in the engine management system to determine whether or not the engine is being fueled on the correct stroke.
The exhaust sensor may be an exhaust gas oxygen sensor, but may be any other sensor capable of detecting changes in the composition of the exhaust gases that relate to a change in the air/fuel ratio in the engine.
These types of sensors are common in the field and can be obtained cheaply. It is also usual for the engine to have an exhaust gas oxygen sensor in the exhaust conduit as part of the engine management system and this method would simply make greater use of it.
The period or frequency of the reversal cycle data may be averaged over a plurality of oscillations in the air/fuel ratio. This reduces the effect of signal noise inherent in real systems so that the data used in comparisons is more reliable.
The period or frequency data of an oscillation in the air/fuel ratio may be ignored by the engine management system if said period or frequency is outside a predetermined range. Large signal errors and instances of open loop control can then be ignored by the engine management system so these errors do not alter the final results.
The engine management system may have a range of pre-determined engine operating conditions during which it calculates the period or frequency of the reversal cycle or the transport delay and stores this for future reference. This avoids errors in readings taken at extremes of the operating range of the engine.
The stored, period or frequency of the reversal cycle or the transport delay is used to calculate an average error for those particular engine operating conditions for which data is recorded. The engine management system is then used to determine whether or not the engine is being fueled on the correct stroke by comparing said temporal characteristics with said relevant engine operation data. This provides the same benefits as the averaging operation described above.
The fuel injection system may be a direct injection system, in which fuel is injected directly in to the cylinders. In a preferred embodiment of the invention, however, the fuel injection system is an indirect injection system in which fuel is injected into an inlet port for each cylinder.
According to another aspect of the invention there is provided a method of operating an internal combustion engine the engine comprising a number of cylinders, the or each cylinder containing a four-stroke reciprocating piston, one or more engine operating condition sensors including an exhaust gas sensor, a fuel injection system, and an engine management system, wherein the engine management system contains engine operation data, the engine operation data being related to expected engine operation with engine fueling on the correct stroke and/or engine fueling on an incorrect stroke, wherein the method comprises the steps of:
a) using the engine management system to control the operation of the engine including the fuel injection system and the air/fuel ratio for at least one cylinder;
b) sending to the engine management system from said sensor(s) respective signal(s) indicative of engine operating conditions, including exhaust gas composition;
c) oscillating the air/fuel ratio between a relatively rich level and a relatively lean level, the exhaust gas composition varying depending on the air/fuel ratio;
d) using the engine management system to reverse the direction of change of the air/fuel ratio when the exhaust gas composition is sensed as being indicative of rich engine operation or lean engine operation;
e) using the engine management system to determine the temporal characteristics of the oscillation in the air/fuel ratio; and
f) using the engine management system to determine whether or not the engine is being fueled on the correct stroke by comparing said temporal characteristics with said relevant engine operation data.